As anthropogenic CO2 raises daily from the massive use of fossil fuels to provide energy for our world population, researchers are becoming increasingly interested in the effects CO2 has on the environment. Of particular concern is the removal of CO2 from the atmosphere as it dissolves into the world's oceans. This process is acidifying the world's oceans, as dissolved CO2 quickly reacts with water to form carbonic acid. How this global ocean acidification is going to impact the biota in the ocean is largely unknown.
Researchers at major universities are utilizing a variety of laboratory and small-scale experiments to explore the biological effects of ocean acidification. The sheer magnitude of the problem, and scarce financial resources to conduct large-scale oceanic sampling, limits the experimental abilities of most scientists. Thus the laboratory approach is a more economical and practical for experimenting with biota which can be maintained in seawater cultures.
One confounding difficulty with experimenting with CO2 effects is that CO2 in the atmosphere naturally varies by season. Photosynthesis during the summer and fossil fuel burning during the winter in the northern hemisphere drive atmospheric CO2 lower and higher by 20-30 ppm. Thus, any experiment that must maintain CO2 concentration for long periods of time must utilize compressed Air/CO2 mixtures or otherwise attempt to overcome the seasonal fluctuation. Moreover, attempting to replicate pre-industrial revolution atmospheric values must use compressed Air/CO2 mixtures. Compressed gases have two detractors: they are reasonably expensive when utilizing large volumes of air that are typically required for healthy culturing, and their stable isotopic fraction is rarely consistent. This severely limits the scope of biogeochemical experimentation for simulating past or future ocean chemistries.
Commonly-used CO2 caustic scrubbers (CO2—CS) utilize acid-base chemistry to remove CO2 from air streams. These CO2—CS scrubbers use a solid phase scrubber media. Unfortunately, the chemical reaction that must take place to remove atmospheric CO2 requires water. While humid air streams can provide some of this water, it often cannot provide enough to fully remove the atmospheric CO2 at high flow rates. Thus, the scrubber looses efficiency by not effectively converting CO2 to carbonic acid, which is then neutralized by the caustic scrubbing media. Further, atmospheric humidity is rarely constant, causing unacceptable changes in CO2—CS scrubber efficiencies. Sprayed water additions can also be used, but even the coating of the water on each of the solid media surfaces is difficult. The capacity of this volume of water is ultimately saturated with the removed CO2 and scrubber breakthrough occurs long before the caustic media is fully neutralized by CO2. The water is still the limiting reactant.
As such, a need exists for a more efficient and consistent CO2 scrubbing system. In addition, to address the experimental shortcomings described above, a system for the stringent control of the partial pressure of CO2 (pCO2) in culture aeration and seawater has been developed.